Yes, dogs have a Jacobson’s organ, also known as the vomeronasal organ. It’s a paired, tube-like structure located at the base of the nasal septum that gives dogs a “second nose” specialized for detecting chemical signals like pheromones. While most people know dogs have an incredible sense of smell, this organ operates as a separate system with its own dedicated pathway to the brain, tuned specifically to social and reproductive chemical cues that the regular nose isn’t designed to pick up.
Where It’s Located
The Jacobson’s organ sits inside a bony canal formed by two small bones on either side of the nasal septum, near the front of the skull. Each side of the organ connects to the roof of the mouth through a small channel called the incisive duct. If you’ve ever looked at the roof of your dog’s mouth, there’s a small bump of tissue just behind the front teeth called the incisive papilla. That bump sits right over the opening to this duct, which serves as the delivery route for chemical signals to reach the organ.
This dual connection to both the nasal cavity and the mouth is key. It means chemical molecules can reach the organ through sniffing or through licking. The organ itself contains specialized sensory cells, bipolar neurons lined along an inner epithelium, that detect these chemical compounds and relay signals to the brain.
What It Detects
The Jacobson’s organ is built to pick up semiochemicals: molecules that carry messages between animals. The most well-known category is pheromones, chemical signals released by one animal that influence the behavior or physiology of another member of the same species. But the organ also detects kairomones (chemical cues from other species, useful for things like predator detection) and molecules tied to the immune system’s major histocompatibility complex, which helps animals assess genetic compatibility in potential mates.
In canids, these chemical signals serve several practical functions: territory maintenance, reproductive synchronization, social hierarchy signaling, maternal recognition of offspring, and even sickness avoidance. When your dog obsessively sniffs another dog’s urine on a walk, they may be gathering a remarkable amount of social data: the other animal’s sex, reproductive status, health, and possibly individual identity.
Researchers believe the organ may also play a role in taste. A 2020 MRI study published in Frontiers in Veterinary Science noted that in dogs, the Jacobson’s organ likely contributes to gustation alongside its chemical signaling role, though this function is still not fully understood.
How Signals Reach the Brain
What makes the Jacobson’s organ truly distinct from normal smell is its wiring. Regular scent molecules travel through the main olfactory system to the olfactory bulb. Chemical signals detected by the Jacobson’s organ take a completely separate route, traveling to a structure called the accessory olfactory bulb, then onward to specific regions of the amygdala, the part of the brain involved in emotional and social processing.
There are actually two subsystems within this pathway, each carrying different types of information to different amygdala targets. One subsystem projects to areas involved in social behavior, while the other connects to regions tied to reproductive and defensive responses. These pathways remain anatomically and functionally separated in the brain, meaning the organ isn’t just feeding general scent data into the same processing pipeline. It’s routing specific types of chemical messages to specialized brain circuits that drive instinctive social and sexual behaviors.
The Teeth-Chattering Behavior
Cats, horses, and many other mammals use a dramatic curling of the upper lip called the flehmen response to push air and chemical compounds into their Jacobson’s organ. Dogs do something different. Because their organ has a direct connection to the mouth through the incisive duct, dogs typically lick a surface first to dissolve and collect chemical molecules, then display what’s called teeth chattering: a rapid clicking or vibrating of the jaw.
This behavior is especially common in unneutered males who’ve just encountered a female dog’s scent, though females do it too when picking up male pheromones. The chattering may be accompanied by foamy salivation. It’s the dog’s equivalent of the flehmen response, a physical action that helps move scent molecules from the mouth up through the incisive duct and into the organ’s sensory chamber. If you’ve ever seen your dog lick a spot on the ground, then lift their head with a strange quivering jaw and a glazed expression, that’s the Jacobson’s organ at work.
Domestication Has Reduced Its Power
Here’s where it gets interesting. Compared to their wild ancestors, domestic dogs have a notably less developed vomeronasal system. A 2024 study in the Journal of Anatomy comparing wolves and domestic dogs found that dogs show limitations in the development of the organ’s sensory lining, poor differentiation of key nerve layers in the accessory olfactory bulb, and a smaller overall organ size. The characteristic cellular architecture found in other mammals with highly functional vomeronasal systems is largely absent in dogs.
One important molecular detail supports this: dogs lack expression of a specific signaling protein (called Gαo) that’s critical for one of the two receptor pathways in the organ. This means an entire class of chemical signals that wolves can detect may be partially or fully invisible to domestic dogs. Researchers believe thousands of years of domestication, during which dogs relied increasingly on human cues rather than chemical communication with other canids, has driven a gradual regression of this sensory system.
That said, the organ is far from nonfunctional. Dogs still clearly respond to pheromones and still display the teeth-chattering behavior. The system works, just not as powerfully as it does in wolves or other wild canids. Research on the vomeronasal system in domestic dogs has grown substantially in the past decade, and scientists continue to map exactly which functions remain intact.
Dogs vs. Humans
Humans technically have a vomeronasal organ too, or at least a remnant of one. Anatomical studies find it in the vast majority of adults, appearing as a small pit in the nasal septum. But that’s where the similarity ends. The human version lacks nerve cells and nerve fibers entirely. Humans also have no accessory olfactory bulb to receive signals from it, and the genes coding for vomeronasal receptor proteins have mutated into nonfunctional versions. The scientific consensus is that the human Jacobson’s organ is vestigial, a leftover structure with no sensory role.
Dogs, by contrast, retain functional sensory neurons, a working (if reduced) accessory olfactory bulb, and active receptor pathways that relay chemical information to the brain. So while both species have the organ, only dogs are actually using it. It’s one more dimension of the chemical world that dogs navigate daily, invisible to us but rich with social meaning for them.